The present disclosure relates to a safety mat for monitoring a technical installation.
As automation of production processes has increased, the requirements in respect of reliable safety of industrial production installations have continuously increased. For example, revised EC Machinery Directive of 17 May 2006 describes a standard safety level for preventing accidents which is to be taken into consideration when a machine is placed on the market or put into service. Accordingly, technical installations, machines and robots may be commissioned only in conjunction with corresponding safety measures. These measures include, in particular, monitoring hazardous regions of a technical installation and moving the technical installation to a state which is safe for persons and objects in the event of unauthorized access to the hazardous region.
So-called pressure or switching mats, as are described in DE 100 46 974 B4 for example, are known from the prior art for identifying the presence of persons. Safety mats of this kind are generally composed of two current-carrying plates which are separated from one another and which are held at a distance from one another by strip- or grid-like spacers. If a person steps on the safety mat, the plates and spacers deform until a cross-connection is formed between the plates. The cross-connection can be detected by measurement and causes a connected safety relay module to switch off the technical installation or to prevent said technical installation from starting up.
This simple sensor system is disadvantageous in many respects. In particular, the size of the safety mat is dependent on the plate size and therefore cannot be extended as desired. Furthermore, the sensitivity of a safety mat of this kind is not homogeneous and varies over the surface area. As indicated in DE 100 46 974 B4, safety mats of this kind generally exhibit their normal sensitivity in the central regions, whereas identification functions only inaccurately or not at all in the border regions. As a result, the safety mats also cannot be lined up with one another in any desired manner in order to protect a relatively large region since large regions in which reliable detection cannot be ensured form at the transitions between the safety mats by virtue of border regions coming together.
Finally, the single safety mat generally does not allow spatially resolving identification. That is to say, it only identifies that the safety mat has been stepped on, but does not identify the region of the safety mat in which this has taken place. However, when monitoring relatively large and relatively complex installations, it would be desirable to distinguish between different hazardous regions in order to allow targeted control of the installation in the event of a hazard. However, this requires an improved sensor system for safety mats.